Conductive pastes are widely used in electronic components because electrode patterns can be formed by printing them. Nowadays, some of the printed patterns are sintered in order to decrease the electric resistance. Contact resistance between powdered metal particles in the conductive paste decreases due to the progress of sintering and thereby resulting printed patterns exhibit higher conductivity. A method is proposed in which an inorganic material such as glass is also added as a binder to achieve secure binding between the patterns and a substrate, and materials for the method are also proposed. For example, Patent Reference 1 discloses a conductive silver paste (conductive paste) composed of silver powder as a main component, SiO2 powder, glass frit (PbO—SiO2), and an organic vehicle. In Reference 1, it is stated that a film is formed by the addition of SiO2 powder during sintering, whereby plating resistance is improved.
As for a glass frit used in the conductive paste, in addition to the lead-containing glass frit described above, a lead-free glass frit is also used (Patent Reference 2). The glass frit is composed of SiO2—Al2O3—B2O3—MgO—CaO, and have a softening point of 580° C. to 800° C.
Another Patent Reference describes individual components used in conductive pastes (Patent Reference 3). Reference 3 states that a precious metal powder is used as a metal powder and that the shape is preferably spherical, with a particle diameter of 0.1 to 3.0 μm. Glass powder described in this Reference contains well-known SiO2, Al2O3, PbO, CaO, and B2O3 as main components, and has a softening point in the range of 450° C. to 650° C. The organic vehicle, which is used, by mixing with the powdered metal and a binder, as a dispersing agent for making the resulting conductive paste suitable for coating, usually contains a solvent, a resin, and an additive. According to the Reference, a preferable solvent is a combination of diethyl phthalate and terpineol, and a preferable resin is a combination of maleic acid resin, ethyl cellulose, and an acrylic resin. Fatty acid amide wax is indispensable for the additive.
Patent Reference 1: Japanese Unexamined Patent Application Publication No. 10-106346
Patent Reference 2: Japanese Patent No. 2941002
Patent Reference 3: Japanese Unexamined Patent Application Publication No. 2003-132735